Thyme leaves turn yellow as a result of root rot, an excess or shortage of nitrogen, or an infestation of spider mites. The most frequent cause of thyme with yellow leaves is root rot, which is brought on by too much moisture around the roots as a result of overwatering or poorly draining soils.
Thyme is a Mediterranean herb that prefers dry soil conditions and will not grow in moist soil, making it vulnerable to root rot.
Yellow leaves on thyme plants frequently have a wilting or drooping appearance, which is another indication of stress brought on by damp conditions, an excess of nitrogen, or roots that are attached to a container.
Learn the cause of your thyme’s yellowing and how to fix it by reading on.
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Thyme Turns Yellow (Over Watering and Slow Draining Soils)
Too much soil moisture around the roots of thyme plants is the most frequent cause of their yellowing, which results from:
- excessive thyme watering.
- soils that drain slowly.
Thyme is a Mediterranean herb that has adapted to the harsh surroundings of a dry, sunny climate with infrequent rainfall. Thyme grows best in sandy soils that are well draining and do not retain moisture.
Thyme’s roots cannot handle constantly moist soil because to its adaptation to arid areas.
Root rot, which can be a common issue for thyme plants and other Mediterranean herbs like lavender and rosemary, is encouraged by moist or damp soil surrounding the roots.
The following are the most typical symptoms of a thyme plant with root rot:
- Brown or yellow leaves.
- a wilted or drooping aspect.
- roots with a dark brown color (rather then a lighter somewhat yellow colour).
Additionally, excessive wetness can promote the growth of fungi that cause the leaves to turn brown. Please read my post Why is my thyme plant going brown to understand how to recover brown thyme foliage.
How to fix it
Your thyme’s yellowing leaves can be stopped and treated with root rot by doing the following:
- Only water thyme once per week in dry weather or every two weeks in wet weather. The best balance of watering thyme in pots and containers is often to give it a nice soak once a week. In most areas, thyme won’t need any watering when planted in garden soil because it can get enough moisture from the surroundings and is drought resistant. Thyme needs to be watered frequently, although the frequency will vary depending on your climate. To ensure strong roots, adjust the frequency of your watering such that the soil surrounding your thyme plant feels fairly dry to a finger’s deep before each bout of watering.
- To promote drainage, add sand or grit to the soil. The sandy soil conditions of the thyme’s original Mediterranean setting are replicated by adding sand or grit to the potting mix or planting location. Sand ensures proper nutritional balance and drainage so that the soil around the thyme can dry out in between waterings, preventing root rot.
- It’s crucial to prune any yellow foliage back to healthy development if the leaves are noticeably yellow and you’ve been watering your thyme too regularly. Examine the roots by carefully removing the thyme from the ground. Snip any rotten, infected, or dark-brown roots to promote healthy growth. To stop the disease from spreading, wipe the pruner blades with a cloth dipped in disinfectant after each snip. Place the thyme in a pot or container with fresh soil that is 70% compost and 30% sand or grit. Give the soil a good soak to lessen transplant shock.
To offer the thyme the best chance for recovery in a few weeks, take the following actions.
To stop the spread of any fungal infections in your garden, I advise discarding or burning the plant if the thyme’s roots are seriously rotting.
With root rot, prevention is typically preferable to treatment, therefore the best course of action is to purchase a new plant, pot it up, and plant it in the proper soil mixture.
Read my post on how to resuscitate a dying thyme plant if your thyme plant has any other issues.
Thyme’s Pot or Container too Small, (Nitrogen Deficiency)
- The container or saucepan is too small (small pots have a limited capacity for soil and therefore nutrients).
- Too much space between the thyme plants (thyme has to compete for space, light, nutrients and water).
As with all Mediterranean herbs, thyme plants tend to prefer pots that are at least 12 inches across so that the roots have room to spread out and have access to nutrients.
Smaller pots and containers have less soil volume, which means they may hold less water and nutrients and provide less room for the roots to spread out, which might influence growth.
Since this is the soil profile of their natural Mediterranean habitat, thyme plants actually prefer low to medium nutrition, sandy soil.
The soil’s nutrients can become scarce if the roots are confined to a container, which causes the thyme to become yellow from a deficiency in nitrogen.
The reason thyme plants can turn yellow if they are planted close together is because they grow naturally in open spaces and do not like to compete with other plants for sunlight, nutrients, airflow, or soil.
How to fix it
Move your thyme to a larger container with drainage holes in the bottom that is at least 12 inches in diameter so that any extra water may drain.
Thyme grows more abundantly and produces leaves with a strong perfume and flavor in larger pots or containers where there is more room for the roots to expand.
A thyme plant can fit all the soil and nutrients it needs for a healthy growth in a pot this size.
Thyme can start to recover from its yellow appearance and convert to a healthy green in a few weeks if you transplant it into a larger container with multipurpose compost and some additional horticultural sand or grit.
As the compost and sand mixture recreates the thyme plants’ native soil conditions with adequate nutrients, do not add any artificial fertilizer as more fertilizer would do more harm than good as thyme prefers poor soil.
Thyme needs full light to grow strong and green, so whether you’re planting it in garden soil or a raised bed, make sure no plants are shading each other out.
Each thyme should be planted at least 18 inches apart (measured from each planting site rather than the outer leaf), as this will provide each plant’s root system ample room to grow and reduce the danger of fungal disease by encouraging good airflow around the leaves.
Your thyme plant with yellow leaves should recover and start to appear more healthy in a few weeks if you plant it in full sun, at a distance, and in a pot that is at least 12 inches across.
Too Much Nitrogen Turns Thyme Leaves Yellow
Both a lack of nitrogen in the soil and an abundance of nitrogen might cause your thyme plant’s leaves to turn yellow. Because thyme plants prefer low to medium fertility soils, they are sensitive to nitrogen in the soil, which is usually caused by fertilizer use. If you have used fertilizer on your thyme, this is most likely the source of yellow leaves.
Thyme plants have evolved to thrive in the nutrient- and water-poor sandy soils of southern Europe.
Therefore, thyme does not need any additional fertilizer to grow healthily in your garden because a high level of nutrients would be in conflict with the natural conditions to which thyme plants have evolved.
An excessive amount of nitrogen in the soil encourages the growth of foliage, which can make a plant appear droopy or wilted and cause the leaves to become yellow as a symptom of stress.
It is crucial to have a decent potting mix with the proper balance of nutrients for thyme to taste and smell its finest. The concentration of essential oils, which impacts the scent and flavor, in the leaves is strongest in plants that are in full light and in soil that is not too nutrient dense.
How to Treat Yellow Thyme Leaves With Nitrogen burn
The solution to thyme leaves becoming yellow from overuse of fertilizer is to:
- Stop using extra fertilizers because they can do more damage than good to thyme.
- Add sand or grit to the soil to amend it.
To replicate the sandy, low to medium soil conditions of the thyme’s natural Mediterranean setting, soil amendment with sand or grit helps to dilute the concentration of nutrients (especially nitrogen).
Sand also facilitates improved soil drainage and increases pore size, which aids in root respiration, therefore having too much sand is preferable to not having enough.
Repot the thyme (or carefully remove it from the ground with a garden fork) and combine 70% multipurpose compost with approximately 30% horticultural sand or grit.
The thyme will have the proper balance of nutrients to thrive and produce aromatic foliage thanks to this mixture of sand and compost. After nitrogen leaf burn, the thyme might take some time to recover, but after a few weeks, it should start to show indications of recovery.
Spider Mites Cause Yellow speckles on Leaves
They frequently go unnoticed even if they are in your garden since they have several insect predators that keep their population in check.
Regardless of the scale, spider mites are rarely a severe problem and may be readily treated. It takes an infestation for them to cause any damage.
If addressed, the damage looks like tiny, yellow dots on the leaves and can lead to leaf drop.
The best course of action if spider mites are turning your thyme leaves yellow is to either blast them off with a hose or, better, remove them by hand.
Usually, this is all it takes to fix the issue as long as you are diligent for a few weeks. Thyme should recover without issues if any damaged foliage is pruned off to encourage new growth.
The imbalance is typically corrected by insect predators in a natural garden, and spider mites may not be a severe repeating issue.
Chemical solutions are still a possibility for solving the issue.
If I’m using a herb for cooking, I try to avoid spraying insecticides or insecticidal soap on the leaves of the plant. However, if spider mites are a persistent issue and your thyme plants are for decoration rather than cooking, you can use an insecticidal soap.
Key Takeaways:
- The most frequent cause of yellowing in thyme plants is root rot brought on by moist soil. Thyme does not tolerate constant dampness and prefers sandy, well-draining soils. Yellow leaves and a drooping or withering appearance are signs of root rot in thyme.
- To increase drainage and mimic the sandy soil characteristics of the Mediterranean region to which thyme is accustomed, add horticultural sand or grit to the soil.
- Thyme can turn yellow if it receives too much nitrogen from fertilizer or too little because of roots that are confined in a pot. To avoid a nitrogen deficiency, plant thyme in a pot at least 12 inches across. Avoid fertilizing the plant because it prefers poor soils and will grow lanky and produce less aroma.
- On fresh growth, spider mites can leave yellow specks. Spider mites can be manually removed or washed off using a hose. To encourage fresh, healthy development, trim off any noticeable damaged growth. If you want to use thyme in cooking, avoid using pesticides.